Potential evapotranspiration (PET) plays a key role in irrigation planning. It provides a daily estimate of the water loss from a well-watered reference crop, based on temperature, wind speed, humidity and solar radiation — offering a baseline to guide irrigation scheduling across varying soil types and crop systems.

In response to a request from the Eastern Plains Land User Group, Tai Tapu Greenpark, Central Plains Water Limited (CPWL) supported the extension of PET coverage across the lower plains through to the Rakaia River. The tool, developed by Aqualinc, now provides daily PET estimates alongside rainfall maps via a simple web interface.

To ensure data quality and usability, rainfall maps are generated through an automated process that includes:

  • Collation of electronic rainfall data from multiple public and private sources;
  • Quality filtering to remove anomalies;
  • Interpolation of site observations, and
  • Presentation of spatial rainfall patterns for the previous day.

By improving access to accurate evapotranspiration and local rainfall data, this initiative supports more informed irrigation scheduling, stronger water-use efficiency, and ongoing environmental improvements across the Selwyn Waihora Zone.